Magnetic recording system

ABSTRACT

An improved magnetic recording system is provided which uses an amplitude-modulated high frequency bias. A first high frequency bias or carrier is amplitude-modulated by a second bias component or modulating wave having a frequency higher than the highest frequency of the input signal but lower than that of the first bias component, and the amplitude-modulated high frequency bias is superposed upon the input signal. The deterioration of the input signal, especially its high frequency component by the prior art unmodulated high frequency bias may be eliminated so that the flat reproduction characteristic may be obtained over the wide range of the input signal. In addition, the improved system requires only the minimum number of component parts.

United States Patent Goshima et al.

[451 Nov. 28, 1972 MAGNETIC RECORDING SYSTEM [72] Inventors: TakeshiGoshima; Yutaka Kohtani, P'imary Examiner-J Russell Goudeau both ofTokyo, Japan AttomeyWard, McElhannon, Brooks & Fitzpatrick [73]Assignee: JCanon Kabushiki Kaisha, Tokyo, [57] ABSTRACT apan l Animproved magnetic recording system is provided [22] Flled' 1971 whichuses an amplitude-modulated high frequency [21] Appl. No.: 106,979 bias.A first high frequency bias or carrier is amplitude-modulated by' asecond bias component or modulating wave having a frequency higher thanthe [30] Forelgn Apph-catmn Pnonty Data highest frequency of the inputsignal but lower than Jan. 21, Japan I. that of the first component, andthe aynplitudemodulated high frequency bias is superposed upon the U-S.Cln .-i-l79/100-2 K sig 1al The deterioration of the signal [51] Int.Cl. ..Gl lb 5/02 especially its high frequency component by the prior[58] Field of Search ..l79/100.2 R, 100.2 K an modulated frequency biasmay be i eliminated so that the flat reproduction characteristic [56] Reerences cued may be obtained over the wide range of the input UNITEDSTATES PATENTS signal. In addition, the improved system requires onlythe minimum number of component parts. 3,262,124 7/1966 Johnson et a1......l79/100.2 K 2,876,294 3/1959 Wissmann 179/1002 R 6 Claims, 5Drawing Figures OSCILLATOR I] A I I8 MODULATOR OSCILLATOR I3 AMP. FILTERvPIITENTEU Nov 28 972 SHEET 1 BF 2 3 OscILLATOR 2 4 ::-5 I S I AMP.FILTER S2 I3 I OscILLATOR A MODULATOR 2 OSCILLATOR I I3 I2 I I4 I I AMP.FILTER I4 v fl6 I l MAGNETIC RECORDING SYSTEM BACKGROUND'OF THEINVENTION The present invention relates to a magnetic recordin g systemand more particularly an improved magnetic recording system in which thehigh frequency component of an input signal may be recorded upon amagnetic recording medium without any deterioration or attenuation.residual The so-called DC and AC bias magnetic recording systems havebeen widely used in the recording of information upon a magnetic tape,magnetic sheet, magnetic drum or the like. Since the 8-H curve or thenormal magnetization curve of the magnetic recording medium isessentially nonlinear, the operating point in the DC bias system isselected from a limited linear portion of the magnetization curve sothat the DC bias with a predetermined level together with the inputsignal may be applied to a magnetic recording head. In the AC biassystem, a bias system having an alternating frequency higher than thatof an input signal to be recorded is superposed upon the input signal atthe magnetic recording head so that the input signal may be recorded asthe vibration in rem'anent magnetism or residual induction upon themagnetic recording medium which is transportedclosely apart from themagnetic head.

Since the magnetization curve is essentially nonlinear as describedabove, the recording will be made along the nonlinear portion of themagnetization curve when the level of the input signal is increased inthe DC bias system so that the recorded signal is inevitably distorted.In the AC bias system, the nonlinear portion of the normal magnetizationcurve may be corrected so that the recording with a higher degree offidelity may become possible. Therefore, the AC bias system isuniversally used in high fidelity audio and video magnetic recording andreproduction. However, the AC bias system has a defect thatthe responseat a higher frequency'range in reproduction is inferior to that in alower frequency range. That is, thehigh frequency characteristic isdeteriorated so that the reproduction with a higher degree of fidelitybecomes impossible. The reason is considered that the high frequencycomponent or the shorter wavelength of the input signal cannot cause thesufficient magnetic variation or variation in residual induction in thedirection ofthe thickness of the magnetic recording medium. In otherwords the high frequency component is recorded as the magnetic variationonly in the surface-layer of the magnetic recording medium so that inreproduction the high frequency component is reduced as compared of thehigh frequency component, so as to minimize the erasing action of thebias current, thereby increasing 'the residual induction for the highfrequency component. However, when the high frequency bias cursystem,there has been proposed another method in which the signal current forthe high frequency component is increased so as to compensate for thehigh frequency response. .This method is effective when the input signalcurrent level is'low, but when the signal a level is high and when theinput signal current is increased for the high frequency component, theresidual induction is reduced. In consequence, in reproduction the highfrequency component is reduced or attenuated. The theoretical analysisofthis phenomenon has not been made yet, but the experience shows thatwhen the signal current for highv frequency component is increased inorder to obtain a flat reproduction characteristic, the high frequencycomponent is reduced in reproduction and the higher the level of theinput signal in recording, the lower the level of the reproduced signalin the higher frequency range becomes. F urthermore, this method ofincreasing the signal current for high frequency component requiresadditional filters, amplifiers and magnetic heads for multi-channelmagnetic recording medium so that a magnetic recording and reproducingsystem becomes complex in structure.

SUMMARY OF THE INVENTION It is therefore one of the objects of thepresent invention to eliminate the effect of the prior art highfrequency bias system.

Another object of the present invention is to provide an improvedmagnetic recording system capable of recording the high frequencycomponent of information or signal to be recorded uponarecording mediumwithout any deterioration or attenuation.

Another object of the present invention is to provide an improvedmagnetic recording system in which upon information or signal to berecorded is superposed an amplitude-modulated high frequencybias signalwhich has a frequency higher than that of information or input signal tobe recorded and which has been modulated by a modulating wave having afrequency higher than that of information or input signal to berecorded.

In brief, in a magnetic recording system in accordance with the presentinvention upon the input signal to be recorded is superposed anamplitudemodulated high frequency bias signal which has a frequencyhigher than that of the signal to be recorded and which has beenamplitude modulated by a modulating wave having a frequency higher thanthat of the signal to be recorded but lower than that of the highfrequency bias signal.

In the high frequency bias system in which a high frequency bias issuperposed upon an input signal current at a magnetic recording head,the bias magnetic field Hf and the magnetic field [-15 due to the inputsignal to be recorded are produced in the air gap of the magnetic head.When the magnetic recording medium passes near the head gap, it alsopasses through the fields Hs and I-Ifso that the residual induction dueto Hs is left upon the magnetic recording medium. Since both 4 of thefields Hf and Hs decrease at a same ratio as the magnetic recordingmedium 'moves away from the center of the head gap, the magnetic signalor residual the air gap. Especially the high frequency component isreduced to a greater extent as described above.

The present invention is based upon this observed fact that the highfrequency vcomponent of signal current is reduced by the fieldl-Ifproduced by the bias current. The l-If component is reduced orattenuated rapidly than the Hs component so that the residual inductiondue to the field Hs upon the magnetic recording medium may not beinfluenced by the I-If component. The system of the present invention issimple in structureand the flat reproduction characteristic may beattained over the whole range.

The above and other objects of the present invention will become moreapparent from the description of the preferred embodiment thereof takenin conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a block diagram of the priorart high frequency bias magnetic recording system;

FIG. 2 illustrate the waveform of superposed input and bias signalsthereof;

FIG. 3 is a block diagramof a magnetic recording I system in accordancewith the present invention;

FIG. 4 illustrates the waveforms of bias signal components I and I andan amplitude-modulated high frequency bias signal I; used in the presentinvention; and

FIG. Sillustrate thewavef orm of superposed input andamplitude-modulated high frequency bias signals applied to a magneticrecording head.

DESCRIPTION OF THE PREFERRED EMBODIMENT Prior Art, FIGS. 1 and2 2Referring to FIG..1 illustrating in block diagram the prior art highfrequency bias recording system, the audio or video signals to berecorded upon a magnetic recording medium are appliedto an inputterminal 1 of an amplifier 2. The high frequency, bias signals generatedby a high frequency bias oscillator 3 are cut off from the amplifier 2by a bias signal cut-off filter 4 and the input signals are cut off fromthe oscillator 3 by a recording signal cut-off capacitor 5. A magnetichead 6 is in contact with the magnetic recording medium (not shown). i

The frequency of the bias signals generated by the oscillator 3 is a fewtimes that of the inputsignals applied at the input terminal 1,amplified by the amplifier 2 superposed upon .the bias signals andapplied to the magnetic record head 6 was to record them upon themagnetic recording medium. The waveform of the rically about the air gapof the magnetic head occurs. As a consequence, the remanent magnetismimpressed upon the magnetic recording medium directly proportional tothe signal to be recorded S is erased by the damping produced bythe-high frequency bias signal outside of the air gap of the magneticrecording head 6. Especially this erasing action is remarkably noted inthe high frequency range of thesignalto be recorded. So

far there has not proposed yet a magnetic recording system in whichthe'magnetic recording characteristic is flat over a wide range. offrequency.

The Present Invention, FIGS. 3, 4 and 5 Next the present invention willbedescribed in detail with reference to FIGS. 3-5. First referring toFIG. 3,

ll designates an ,input terminal to which is applied a signal to berecorded; 12, an amplifier for amplifying the signal to be recorded; 13,a high frequency bias signal oscillator; 14, a bias signal cut-offfilter; l5, a capacitor for cutting off the signal to be recorded; 16, amagnetic recording head; 17, a modulating wave generatingoscillator;'and 18, an amplitude modulator.

Theamplitude modulator 18 has a function of am-- plitude-modulating thebias signal current from the high frequencybias generator 13 by theoutput current I from the modulating wave generating oscillator 17. Thefrequency f; of the bias signal current I is selected sufiicientlyhigher than the frequency f of the modulating wave 1 that is f, f. Thepercentage modulation of the modulator 18 is preferably percent(modulation degree l), which is not necessary as far as the percentagemodulation is close to 100 percent.

As to the frequencies f, and f of the outputs from the high frequencybias generating oscillator 13 and the modulating wave generatingoscillator 17 are for example 300 KHZ and 60. KHz respectively when theaudio signal with the highest frequency of 20'KI-Iz is applied to theinput terminal 11. Both of the high-frequency bias generating oscillator13 and the modulating wave generating oscillator 17 may be of theconventional type oscillator.

As shown in FIG. 4, the output current I from the oscillator 13 isamplitude-modulated with the modulating wave I .from the oscillator 17by the modulator 18 to produce output wave l The input current I isamplified by the amplifier 12 and the amplified current I, is superposedupon the amplitude-modulated current I which is applied through thecapacitor 15, so that the current 1,, having the waveform as shown inFIG. 5 is applied to the magnetic recording head 16 whose airgap is madein contact with the magnetic recording mediumas with the case of themagnetic head 6 in FIG. 1

When the'signal current I,, is applied to the magnetic recording head16, the remanent magnetism is im- -pressed upon the magnetic recordingmedium by the magnetic field Hs generated by the electrical signal I inthe air gap of the magnetic recording head 16, thus leaving upon themagnetic recording medium a series of magnetized sections whichcorrespond to the electrical signal I, applied to the head 16 when thehead gap was in contact with the recording medium at each of thesections. In this case, the bias magnetic field Hf produced by the biascurrent I is immediately decreased, only leaving the field Hs. As aconsequence,

the magnetic field Hf, which is gradually decreased, does not exist inthe proximity of the air gap of the magnetic head so that the remanentmagnetism left upon the magnetic recording medium by Hs will not beerased by Hf. Thus only the remanent magnetism corresponding to theelectrical signal 1 is left upon the magnetic recording medium. There isno defect that the signal to be recorded I,,, especially its highfrequency component is deteriorated. In other words, the defect of theprior art that the signal to be recorded is erased may be eliminated sothat the high frequencycomponent of the signal to be recorded I is notattenuated at all when recorded upon the magnetic recording medium. As aconsequence, the magnetic recording characteristic which is flat overthe wide range of the frequency of the signal to be recorded may beobtained.

The best result will be attained when the percentage modulation of theamplitude modulator 18 is IOOpercent, but the better result may be alsoobtained by a percentage modulation less than 100 percent.

ln summary, the present invention utilizes the modified bias signalwhich is obtained by amplitude modulating the high frequency bias signalby a signal having a frequency higher than that of the informationsignal to be recorded and superposes this modified bias upon the signalto be recorded at the magnetic recording head so as to magneticallyrecord the signal to be recorded upon the magnetic recording medium.Therefore, the signal recorded upon the magnetic recording medium as theremanent magnetism corresponding to the input signal will not be erasedat all by the high frequency bias signal so that the input signal may berecorded upon the magnetic recording medium with a higher degree offidelity.

As described above, the present invention utilizes theamplitude-modulated bias signal instead of the high frequency bias ofthe prior art system so that the magnetic recording with a betterfrequency characteristic without the attenuation of the high frequencycomponent of the signal to be recorded becomes possible. In addition,the system of the present invention is simple in structure. The systemof the present invention is therefore very effective and advantageous inthe magnetic recording and reproducing system.

In the present embodiment, the magnetic recording head has beendescribed as being the conventional magnetic head consisting of a magnetcore carrying a coil so that the magnetic recording may be madeupon themagnetic recording medium by the variation in flux leaked from the airgap. However, it is understood that the present invention is not limitedto this type of the magnetic recording head and that otherelectro-magnetic transducers for converting the electrical signal intothe magnetic signal such as the Hall effect element without the use ofcoils may be also employed in the system of the present invention.

In the present embodiment, the signals have been described as being thecurrents, but it is understood that the voltage signals may be alsoused.

What is claimed is: l. A magnetic recording system for recording asignal upon a magnetic recording medium comprising means for providingan input signal to be recorded, a high-frequency signal source,

a modulating signal source for providing a modulating signal having asubstantially constant frequency which is lower than said high frequencysignal but higher than the highest frequency of said input signal to berecorded,

amplitude-modulating means coupled to said high frequency source andsaid modulating signal source for providing an amplitude-modulated highfrequency bias signal by modulating said high frequency signal with saidmodulating signal,

means for superposing upon said input signal to be recorded saidamplitude-modulated high frequency bias signal, and

means for applying said superposed signals to an electromagnetictransducer means in contact with a magnetic recording medium. v

2. A magnetic recording system according to claim 1 wherein said highfrequency signal source and said modulating signal source providesinusoidal waves so that the amplitude-modulated high frequency biassignal is a sinusoidal high frequency signal whose envelope issymmetrically increased and decreased repetetively 3. A magneticrecording system according to claim 2 wherein said amplitude modulatormeans comprises means for providing a percentage modulation which isabout 100%.

4. A magnetic recording device for recording a signal upon a magneticrecording medium characterized by a first oscillator for generating ahigh frequency signal having a frequency higher than that of an inputsignal to be recorded,

a second oscillator for generating a modulating wave having a frequencylower than that of said high frequency signal and higher than thehighest frequency of said input signal to be recorded,

an amplitude modulator electrically coupled to said first and secondoscillators for amplitude-modulating said high frequency signalgenerated by said first oscillator by said modulating wave to therebyproduce an output bias signal,

a circuit for applying said input signal to be recorded,

a superposition circuit electrically coupled to said amplitude modulatorand said signal applying circuit for superposing the output of saidamplitude modulator upon the output of said signal applying circuit, and

an electromagnetic transducer means in contact with a magnetic recordingmedium, the output of said superposition circuit being applied to saidelectromagnetic transducer means so that the electrical signal from saidsuperposition circuit may be converted into the magnetic signal so as tobe recorded upon said magnetic recording medium as the remanentmagnetism.

5. A magnetic recording device according to claim 4 wherein saidsuperposition circuit has a filter for isolating said input signal to berecorded, which is interposed between the output terminal of said signalapplying circuit and said amplitude modulator, and a bias signalisolating filter,-both of said filters being coupled to said transducermeans.

v 6. A magnetic recording system according to claim 4 wherein said firstand second oscillators produce-- sinusoidal waveform-signals, and theoutput of said first oscillator is amplitude-modulated at a percentagemodulation of about 100 percent by said amplitude modulator.

1. A magnetic recording system for recording a signal upon a magneticrecording medium comprising means for providing an input signal to berecorded, a high-frequency signal source, a modulating signal source forproviding a modulating signal having a substantially constant frequencywhich is lower than said high frequency signal but higher than thehighest frequency of said input signal to be recorded,amplitude-modulating means coupled to said high frequency source andsaid modulating signal source for providing an amplitudemodulated highfrequency bias signal by modulating said high frequency signal with saidmodulating signal, means for superposing upon said input signal to berecorded said amplitude-modulated high frequency bias signal, and meansfor applying said superposed signals to an electromagnetic transducermeans in contact with a magnetic recording medium.
 2. A magneticrecording system according to claim 1 wherein said high frequency signalsource and said modulating signal source provide sinusoidal waves sothat the amplitude-modulated high frequency bias signal is a sinusoidalhigh frequency signal whose envelope is symmetrically increased anddecreased repetetively
 3. A magnetic recording system according to claim2 wherein said amplitude modulator means comprises means for providing apercentage modulation which is about 100%.
 4. A magnetic recordingdevice for recording a signal upon a magnetic recording mediumcharacterized by a first oscillator for generating a high frequencysignal having a frequency higher than that of an input signal to berecorded, a second oscillator for generating a modulating wave having afrequency lower than that of said high frequency signal and higher thanthe highest frequency of said input signal to be recorded, an amplitudemodulator electrically coupled to said first and second oscillators foramplitude-modulating said high frequency signal generated by said firstoscillator by said modulating wave to thereby produce an output biassignal, a circuit for applying said input signal to be recorded, asuperposition circuit electrically coupled to said amplitude modulatorand said signal applying circuit for superposing tHe output of saidamplitude modulator upon the output of said signal applying circuit, andan electromagnetic transducer means in contact with a magnetic recordingmedium, the output of said superposition circuit being applied to saidelectromagnetic transducer means so that the electrical signal from saidsuperposition circuit may be converted into the magnetic signal so as tobe recorded upon said magnetic recording medium as the remanentmagnetism.
 5. A magnetic recording device according to claim 4 whereinsaid superposition circuit has a filter for isolating said input signalto be recorded, which is interposed between the output terminal of saidsignal applying circuit and said amplitude modulator, and a bias signalisolating filter, both of said filters being coupled to said transducermeans.
 6. A magnetic recording system according to claim 4 wherein saidfirst and second oscillators produce*sinusoidal waveform signals, andthe output of said first oscillator is amplitude-modulated at apercentage modulation of about 100 percent by said amplitude modulator.